a) Field of the Invention
This invention relates to an efficient method for preparing methylene bis (6-benzotriazolylphenols), in particular 2,2'-methylene-bis-[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)- phenol]. The method allows rapid recovery of very pure product.
b) State of the Art
2,2'-Methylene-bis-[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)-p henol] is a known material having utility as an ultraviolet light absorber. It has been the subject of a number of patents including U.S. Pat. No. 4,937,348 (the "'348 Patent"). According to the '348 Patent, alkylidene bisphenols, such as 2,2'-methylene-bis-[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)- phenol], may be prepared by (i) reacting a 4-hydrocarbyl-6-benzotriazolyl phenol with a primary or secondary amine and formaldehyde in an inert organic solvent to produce a Mannich base and (ii) reacting the base with itself or a 4-hydrocarbyl-6-benzotriazolyl phenol, preferably in the presence of an alkaline catalyst, such as a lower alkali metal alcoholate, an alkali metal hydroxide or an alkali metal alkaline salt. The reactions are carried out between 20.degree. C. and 200.degree. C., preferably between 30.degree. C. and 150.degree. C. The patent teaches removal of the solvent between steps (i) and (ii) to isolate the crude intermediate.
Preparation of 2,2'-methylene-bis-[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)- phenol] is described in Example 3 of the '348 Patent. According to the process 4-(1,1,3,3-tetramethyl)butyl-6-benzotriazolyl-phenol was reacted with a secondary alkyl amine and paraformaldehyde in butanol and heated at reflux temperature for 24 hours. The solvent was distilled off. The resulting Mannich base and 4-(1,1,3,3-tetramethyl)butyl-6-benzotriazolyl-phenol were dissolved in xylene and sodium methylate was added. The solution was heated under reflux at 140 to 150.degree. C. for ten hours with a stream of nitrogen. The solvent was distilled off. The residue was recrystallized from xylene and then from n-heptane to produce a product melting at 200.degree. C.
In contrast to the prior art processes, the present invention is more efficient and simpler. The entire reaction can be effected more rapidly in a single reaction vessel. Surprisingly, it has been found that by allowing the condensation of the formaldehyde and the amine to proceed before adding a solvent, the time required for the reaction is significantly reduced.